Stop motion



June 21, 1955 A. EDELMAN ET Al. 2,711,094'

sToP MOTION Filed June 25, 1949 3 Sheets-Sheet l ANS LUSTIG.

` ATTORNEYS,

June 21, 1955 A. EDELMAN ETAL 2,711,094

sToP MOTION Filed June 25, 1949 s sheets-sheet 2 INVENToRs. 'ABRAHAM EDELMAN,

ROBERT H. ROUGHSEDGE B HANS G. LUSTIG` M VMM/Mq ATTORN Eys.

June 2l, 1955 A. EDELMAN rl-:TAL

STOP MOTION 5 Sheets-Sheet 3 Filed June 25, 1949 DGE E 1 SN 02% WMWG. L OT MMR@ MEHL M Mm@ Aem ARH Y B am" lili "W ,a n w .M n y J JIS? Ll H 2l w wf 1 H .vh wn MQ.

ATTORNEYS United States Patent() 2,711,094 STOP MTION Abraham Edelman, New York, N. Y., Robert H. Roughsedge, Ramsey, N. J., .and Hans G. Lustig, New York, N. Y., assignors to Celanese Corporation of America, New York, Y., a corporation of Delaware Application June 25, 1949, Serial No. 101,404 32 Claims. (Cl. 66-166) This invention relates to stop motions and relates more particularly to photoelectric stop motions for warp-knitting machines.

In textile machines wherein fabrics are being produced, it is desirable to provide a stop motion which will give a warning or stop such machines whenever ka fabric defect occurs. Most of the stop motions hitherto proposed for this purpose have been actuated by the breakage of a yarn going into said fabrics and, as a result, they have failed to operate when a fabric defect was produced by any cause other than a broken yarn. Moreover, these stop motions occasionally failed to operate when a yarn break did occur, permitting the production of a fabric containing defects.

It is an important object of this invention to provide a stop motion which will be free from the foregoing and other disadvantages of the prior stop motions, and which will be especially efficient in operation and simple in construction.

A further object of this invention is the provision of a photoelectric stop motion which will not respond to spurious signals and will not require frequent readjustment, but which will operate consistently to give a warning or stop the textile machine to which it is connected whenever a fabric defect occurs.

Other objects of this invention, together with certain details of construction and combinations of parts, will be apparent from the following detailed description and claims.

In accordance with this invention, there is provided a photoelectric stop motion, comprising means for illuminating a fabric, a pair of phototubes which are directed toward different portions of the fabric, means for traversing the phototubes across the illuminated fabric to scan the same and an amplifier connected to the phototubes, which amplifier is constructed so that it is responsive to the difference inthe signal from the phototubes caused by the Variation in the intensity of the light coming from the fabric to the phototubes when one of the phototubes scans a fabric defect. For narrow fabrics, a single pair of phototubes will of the fabric. For wide fabrics, on the other hand, several pairs of phototubes may be employed to give a greater coverage of the fabric for a given speed of traverse, which has the merit of decreasing the length of the fabric containing defects which can be produced before the defects are detected.

Each pair of phototubes is mounted in a reciprocating carriage that is supported by shock-absorbing mounts to minimize the transmission of mechanical shocks and vibration to the phototubes. Also mounted in the carriage are preamplifier tubes to strengthen the signals from the phototubes before said signals are carried through a suitable electrical connection from the carriage to the amplifier. In this way, the relative amplitude of random signals or noise introduced into the desired signal by stray electric and magnetic fields is reduced. The carriage drive is equipped with shock-absorbing means for reducing the acceleration on the carriage and the components mounted therein upon reversals, which serves to lower the amplitude of any random signals or noise caused by such acceleration. With the amplitude of random signals or noise kept to a minimum, smaller true signals give an adequate coverage can be distinguished, permitting the use of a smaller light source than would normally be required and the detection of fabric defectsrof very small magnitude.

vWhen several pairs of phototubes are employed to scan a fabric, the carriages in which said pairs of phototubes are mounted may be driven from a common source or they may be driven independently. The speed at which the carriage is traversed across the fabric controls the duration or" the wave front produced when a phototube scans a fabric defect, such as a missing thread, which duration is unaffected by the size of the defect. In order to minimize the length of a fabric containing defects which can be produced before the defect is detected, the speed of traverse is made as high as is consistent with the particular mechanical design employed.

The means for illuminating lthe fabric may be positioned on the opposite side of the fabric from the phototubes so that the light passes through the fabric before striking the phototubes. However, it is preferred to position the means for illuminating the fabric on the same side of the fabric as the phototubes, and scan the fabric by reflected light. If desired, a reflecting surface may be positioned on the side of the fabric opposite the phototubes to increase the amount of light reflected to the phototubes when the illuminating means and the phototubes are positioned on the same side of the fabric. The fabric may be illuminated generally by lamps that are fixed or that are traversed with the phototubes. Alternatively, the fabric may be illuminated with a lamp or lamps Whose light is focused into a beam that is traversed across the fabric with the phototubes. To illuminate the fabric, it is preferred to employ lamps ofthe incandescent type having heavy tungsten filaments possessing a high thermal inertia, such as automobile headlight lamps, so that the light output of :the lamps cannot change at a rapid rate with variations in lamp Voltage. To assis-t further in maintaining the light output constant, :the lamps are preferably energized by direct current, which is filtered to remove any cyclic variations therefrom.

The light coming from the fabric is focused by suitable 'optical means onto masks positioned in front of each of the phototubes, which masks are-provided with openings that determine the area of the fabric being scanned; The openings are preferably kin the form of slits extending lengthwise of the fabric and are suiiiciently long so that the length of the fabric produced between the successive passages of the phototubes is fully scanned. Shutters may be provided to adjust the width of the slit to pass the light from one, two, three or more-yarns, as desired, and to insure that the direction of the slit corresponds to that of the yarns so that there will be a maximum effect when a yarn is missing or doubled or some other defect exists in the fabric. When the light coming from the fabric is directed onto the phototubesin this manner, a slight amount of defocussing, such as occurs when the fabric and the phototubes move toward or away from each other, is unimportant. n The phototubes are preferably positioned in line with each other along the line of traverse so that a fabric defect which comes into the 'View of one phototube does not simultaneously come into the View of the other phototube. instead, each area of thefabric is scanned twice and a fabric defect will produce a signal from each phototube in succession, if the first signal should fail to operate the stop motion. After being amplified by the preamplifier tubes the signals are fed into a comparison circuit, wherein electrical surges, line voltage fluctuations and the residue of any cyclic variations in lamp current are balanced out since they affect both phototubes in the same way. Thus, each phototube acts as a reference for the other and so long as both phototubes are affected in the same manner there will be no difference between them. The circuit in which the output signals of the preamplifier tubes are compared is designed so that it always tends toward equilibrium or zero output. As a result, this circuit automatically compensates for any slow changes or any permanent or semi-permanent differences in the output signals from the preamplifier tubes, which may be caused by differences in the illumination of the areas of the fabric viewed by each phototube or by difierences in the sensitivity of the phototubes and the prearnplifier tubes. it is, therefore, unnecessary to make the illumination on the fabric perfectly uniform or to employ precisely matched phototubes and preamplifier tubes, or to make adjustments to compensate for the unequal variations of the components due to any cause, such as age, for example.

The signal resulting when a fabric defect is scanned by one of the phototubes is differentiated in the comparison circuit creating both a negative and a positive pulse. ln this way, the scanning of a fabric defect which causes the amount of light striking the phototube to be increased, and the scanning of a fabric defect which causes the amount of light striking the phototube to be decreased, each create pulses of both polarities, which can be handled alike. Similarly, the scanning of a fabric defect by either phototube, or in either direction, also creates pulses of both polarities. The pulses are filtered to remove therefrom extremely slow and extremely rapid variations which cannot represent a fabric defect. The pulses are also compared with a reference voltage. lf Athe pulse is larger than this voltage, it passes through the circuit. Otherwise, it is completely suppressed. The sen sitivity of the stop motion may be adiusted readily by altering the value of this reference voltage. The pulse is Y then lengthened and amplified in a power amplifier, and the current from said amplifier is employed to give a warning or to cause the textile machine to which the stop motion is connected to stop. When the cause of the fabric defect has been corrected, the textile machine may be put back into operation without the necessity for resetting the photoelectric stop motion in any way. Time delay means may be provided to render the stop motion inoperative for a predetermined interval after the textile machine is put back into operation, thereby avoiding the repeated operation of the stop motion as the phototubes scan the fabric defect which first caused the stop motion to operate.

Because it is not mechanically feasible to stop the carriage in which the phototubes are mounted when the phototubes have scanned the fabric precisely to its edge, it is preferred instead to permit the phototubes to scan pastthe edge of the fabric before their motion is reversed and to provide means controlled by the position of the carriage to render the stop motion inoperative when the scanned area goes off the fabric. This also prevents variations in the end positions of the carriage from adversely affecting the operation of the stop motion. Similar means controlled by the position of the carriage may be provided to render the stop motion momentarily inoperative when the phototubes scan a portion of the fabric which contains a normal structure that would give a defect signal, such as a black yarn in a white fabric.

in warp knitting machines, the edges of the fabric tend to curl and shrink as the fabric leaves the knitting elements. This tendency, if unchecked, prevents the scanning of the fabric edges and may distort the fabric suliiciently adjacent the edges to produce a spurious operation of the stop motion. The edges of the fabric may be iiattened and stretched to the full width by any suitable means, such as tenter belts, to prevent such spurious operation.

The stop motion of this invention is particularly useful with fabrics containing patterns. In such case, the phototubes are spaced aparta distance equal to an integral number of pattern widths, so that each phototube views a corresponding portion of the pattern. Both 4 phototubes, therefore, simultaneouslyV receive the same amount of light from the fabric until a defect occurs, al-

though the quantity of light striking the phototubes may vary greatly as different portions of the pattern are scanned. The spacing between the areas of the fabric scanned by each phototube may be made adjustable to permit the adaptation of the stop motion to fabrics having patterns of different size. When the fabrics contain a lacy pattern having many openings or thin spots therein, it may be desirable to have the phototubes view the fabrics from an angle other than a right angle to obtain an improved contrast between a normal fabric and one containing -a defect. Otherwise, it is preferred to have the maximum intensity of light therefrom.

The photoelectric stop motion of this invention produces the best results when pairs of phototubes are employed therein. However, satisfactory results may also be obtained with fabrics that do not have a pattern by using a single phototube and passing the signal from this phototube through the amplifier described herein.

While the iiuctuations produced by electrical surges, p

be described in connection with the accompanying drawing, in which Y Fig. 1 is a side elevational view .of a warp knitting machine,` showing the scanning device of our invention Y applied thereto, I

Fig. 2 is a detail view, on an enlarged scale, Lshowing the scanning device carriage in which the phototubes are mounted and the mounting therefor,

in Fig. 2,

Fig. 4 is a front elevational view of the housing in which the phototubes are mounted,

Fig. 5 is a side elevational view of the housing shown-` 4 3 in Fig. 4, i v Fig. 6 is a schematic diagram of the amplifier circuit,

and

Fig. 7 is a plan view showing the scanning of terned fabric.

VJ the several views of the drawings.

Referring now to the drawings, the reference numeral 11 designates the frame membersfof a two-bar Warp knitting machine on which are supported warp beams 12 and 13 and tension rods 14 and 15 over'which warps 16 and 17 are passed on their way to knitting elements indicated generally by reference numeral 18. These knitting elements, as is well understood in the art, are operated from the cam shaft 19 and knit the warps Y16 and 17 into a fabric 21 which .passes over guide rod 22, under roller 23 and on to take-up roller .24.

A rectangular rail 25, formed from side plates 426y and upper and lower plates 27, is supported onbrackets 28 and 29 fixed to the frame members. Mounted on the rail 25 is a carriage, indicated generally by reference is carried by rubber covered pulleys 33, 34 and 35 that engage the rail 25 and absorb a portion of the mechanical shocks and vibration which would otherwise be trans- Brackets 36carrying plates 37 the plates 37 and Yact to'prevent the transmission ofnie-y chanical shocks and vibration to the phototubes 39 and phototubes view the fabric at `right `angles to receive the A preferred embodiment of my photoelectrici stop mo` tion applied to a two-bar warp knitting machine will nowy Fig. 3 is a front elevational view of the carriage shown n a .pat-.r a

Like reference numerals indicate like parts throughou l numeral 31. The carriage 31 comprises a bar 32, which 5 preamplifier tubes 41. Light coming from the fabric 21 is focused by means of lenses 45 onto masks 46 having apertures 47 therein, which masks are positioned in front of each of the phototubes 39. The carriage 31 also includes a strap 48 depending from the bar 32, which strap 43 successively actuates switches 49 and 51 fastened to the rail 25 to render the stop motion inoperative when the phototubes 39 reach one edge of the fabric 21 and to reverse the direction in which the carriage 31 moves. fabric 21 by means of a cable 52 that is operated by a reversible motor 53 controlled by the switch 49, which motor drives a pulley Sd, around which the cable 52 is wrapped, through a speed reducer 5S. The cable 52 has a spring 56 mounted therein to reduce the acceleration on the carriage 31 when the motor 53 is reversed thereby to reduce the shock on the components mounted in the housing 38. A pair of switches, not shown, similar to the switches 49 and 51, is provided at the other end of the rail 25 to render the stop motion inoperative when 3g the phototubes 39 reach the other edge or the fabric 21 and to again reverse the direction of movement of the p carriage 31.

Referring now to Fig. 6 of the drawings wherein the circuit of the photoelectric stop motion is shown, the

phototubes 39 have their anodes connected to the plates and their cathodes connected to the control grids of the preamplifier tubes 41. The cathodes of the preamplifier tubes 41 are connected to ground through a bridge comprising resistors 57 and SS in one leg and a resistor 59 5 l and a variable resistor 61 in the other, and the control grids of said preamptlier tubes are connected to ground through resistors 62. With these connections, the potentials of the cathodes of the preamplifier tubes 41 follow the potentials of the control grids, and the change in relative potential between the cathodes andthe control grids is small, even when signals of considerable magnitude occur.

The phototubes 39 and preamplifier tubes il are shielded from magnetic and electrical fields by magnetic shields 63 and electrostatic shields 64. These shields may k be combined by using a conductive iron or steel housing, but at some sacrice in shielding efficiency. in addition, each phototube 39 is enclosed in an inner optical and electrical shield 65, which is insulated from ground and connected to the cathode of the preamplifier tube 41. The shields 65 have a suitable opening for passage of light from the fabric 21 to the light sensitive element of the phototube 39. Since the potential variations of the cathode of the preamplifier tube 41, to which the shield 65 is connected, follow the potential variations of the control grid of said preamplifier tube, the potential difference on the capacitor formed between the phototube 39 and its wiring, on one side, and the shield 65, on the other side, remains substantially constant. As a result,

no large charging current for this capacitor need flow to the phototube 39 through the grid circuit Wiring of the preamplifier tube 41. If the inner shield 65 were omitted, as is usually done, or if the inner shield were grounded, the changes in the grid potential of the preamplifier tube 41 due to a signal from the phototube 39 would require that the capacitor formed between the phototube 39 and its surroundings be charged or discharged to match the grid potential. This would force a charging curernt to fiow through the grid circuit Wires of the preamplifier tube 41 and inuence the grid of said tube adversely. The effect of this charging current would be to prevent a quick response of the preamplifier tube 41 to signals from the phototube 39, reducing the overall sensitivity of the amplifier.

During operation, a positive voltage is applied to the anodes of the phototubes 39 and the plates of the preamplifier tube 41. This voltage is divided between the resistor 62 and the phototube 39 in accordance with the intensity of the light striking the phototube at each instant. When one of the phototubes 39 scans a fabric defect The carriage 31 is traversed across the which decreases the amount of light striking the phototube, the current through the phototube diminishes and the voltage across the resistor 62 diminishes, since this voltage is due solely to the current fiowing through the phototube. The drop in the voltage across the resistor 62 swings the grid of the preamplifier tube 41 connected thereto negatively, causing the cathode of said preamplifier tube to swing negatively by the same amount. In like manner, the cathode of the preamplifier tube 41 swings positively when the amount of light striking the phototube 39 increases as the phototube leaves the fabric defect. When the phototube 39 scans a fabric defect which increases the amount of light striking the phototube, the sequence of theisignals will be reversed with the positive swing preceding the negative. Since each area on the fabric is scanned by both phototubes 39, a similar set of' pulses will be produced from each phototube if the paises from one phototube should fail to operate the stop motion.

T he cathode potentials of the preamplifier tubes 41 are compared in aV series circuit comprising a capacitor 65 and primary winding 66 of a transformer 6'7 having a secondary winding 6g, which circuit is connected at one end between the resistors 57 and 5S and at the other end between the resistor 59 and the variable resistor 61. By adjusting the variable resistor 61, which acts as a balance control, it is possible to equalize the effect of line voltage fiuctuations, electrical surges, vibrations, etc. A perfect adjustment of the variable resistor 61 is not necessary, since any permanent unbalance simply results in a steady voltage across the capacitor 65', but does not cause a current to flow through said capacitor and the primary winding 66. However, when one of the phototubes 39 scans a fabric defect and causes the cathode of the preamplifier tube 41 connected thereto to swing negatively, a signal current flows through the capacitor 65 and the primary winding 66 in one direction until the voltage across said capacitor has been changed by an amount equal to the change in cathode potential. Similarly, when the phototube 39 causes the cathode of the preamplifier tube 4l connected thereto to swing positively, a signal liows through the capacitor 65 and the primary winding 66 in the other direction until the voltage across said capacitor has again been changed by an amount equal to the change in cathode potential. The capacitor 65 thus acts to differentiate any change in the cathode potential of the preamplifier tubes d1, so that the scanning of a defect by either phototube 39 produces a signal current in both directions through the primary winding 66. A similar differentiating effect may be obtained from the transformer 67. As a result, the amplifier need be responsive to a signal of only one type. The magnitude of the current flowing through the primary winding 66 depends upon the rate of change of the difference in potential between the cathodes of the preamplifier tubes 41. Accordingly, when the difference in potential between the cathodes of the preamplifier tubes 41 varies more slowly than a predetermined minimum, representing the signal produced by the scanning of a fabric defect, the current flowing through the primary winding 66 is very small and will not cause operation of the photoelectric stop motion, as will be described more fully hereinafter.

The signal produced when a fabric defect is scanned passes through the transformer 67 to the control grid of an amplifier tube 69, which is biased negative almost to cut-off. Because of' the high negative bias on the control grid of the amplifier tube 69, negative polarity signals have little effect on the plate current of said tube, but positive polarity signals cause a marked increase in late current. This increase in plate current causes a negative signal to be applied to the control grid of an amplitier tube 7G, which is biased slightly negative so that maximum plate current fiows through it normally with no signal. Because of the slight negative bias on the control grid of the amplifier tube 7i), positive polarity signais have little effect on the plate current of said tube, but negative polarityV signals cause a marked decrease in plate current. The polarity and biasing arrangements of the amplifier tubes 69 and 7l) make the amplifier selectively responsive to signals of one polarity and greatly decrease the responsiveness of the amplifier to signals of dierent polarity. Any signals that vary more rapidly than a predetermined maximum, representing the scanning of a fabric defect, are lay-passed to ground by capacitors 7l, which are connected to the plates of the amplifier tubes 69 and '7b. Thus, the capacitors 7i act a filtering means for eliminating signals having a frequency outside a predetermined range. As a result, these rapidly varying signals have only a slight effect on the plate current of the amplifier tube 7i) and do not cause operation or the photoelectric stop motion, as will be described more fully hereinafter.

The decrease in the plate current of the ampliiier tube 7i) when a fabric defect is scanned causes a positive signal to be applied to the control grid of a clipper tube 72;, which is biased beyond the cut-oli point so that no current normally flows through its plate circuit. When the amplitude of the positive signal applied to the control grid of the clipper tube 72 is sumciently great, a current iiows momentarily through the plate circuit of said tube. However, when the amplitude of the positive signal applied to the control grid ot the clipper' tube 72 is less than a predetermined minimum, such as results from extremely slow or extremely rapid variations in light intensity, no current flows in the plate circuit of said tube, The amplitude of the positive signal necessary to cause a current to iiow in the plate circuit oi the clipper tube '72 depends upon the bias voltage applied to said tube and may be controlled by means of a variable resistor 73, which acts as a sensitivity control. Connected in the circuit leading to the control grid of the clipper tube 72 is the switch '39, w ch when closed prevents any signals from reaching the control grid, rendering the stop motion inoperative when the phototubes 39 scan past the edge of the fabric 21.

The momentary flow of current in the plate circuit of the clipper 72 causes a large increase in the charge on a capacitor 74 connected in series with said plate. fter the flow of current in the plate circuit of the clipper tube 2 ceases, the capacitor 74 discharges slowly through a resistor 75', connected across its terminals, whose resistance is selected so 'that it takes approximately 0.3-0.4 second for the capacitor to discharge. During the interval of time for which the capacitor 74 has a charge thereon, there is a negative signal applied to the control grid of a power amplifier tube 76, interrupting the ow of current in the plate circuit of said tube, which circuit includes a relay coil '77 shunted by a capacitor 73. The interruption of the current through the relay coil 77 releases the contacts 79 to stop the textile machine to which the stop motion is connected or to give a warning that a l'abric defect exists.

The power supply for the ampliiier includes an alternating current power line Si, which is connected to the primary winding 82 or" a transformer 33 having secondary windings Sd, 8S, 86, $7 and Sti. The secondary winding 84% is connected to a bridge rectifier S9, which furnishes current to the lamps 42 and the filaments of the preamplifier tubes 41 and the amplifier tubes 69 and 'itl through a lter comprising capacitors 91 and choke coils 92. Filtered direct current is used on the filaments of the preamplilier tubes Il and the amplifier tubes 69 and 7i to minimize the ripple which would otherwise be introduced into the amplifier. The filaments of the other vacuum tubes in the amplilier are supplied with alternating current from the secondary wind.

ing 86. The high voltage supply for the amplifier is obtained from the secondary winding E7, which is connected to a full-wave rectifier 3, whose filament is energized from the secondary' winding SS. After being rectified, the high voltage is filtered by capacitors 94 and choke coil 95. The high voltage supply furnishes current to the phototubes 39 and preamplifier tubes 4l through a dropping resistor 96 and also furnishes current to the amplifier tubes 69 and 70 and to the clipper tube 72. A voltage stabilizing tube 97 is connected across the high voltage supply to assist in maintaining a constant voltage on the amplifier. Current for the power amplilier tube 76 is furnished from the secondary winding 85 without rectification or iiltering through the terminals 98.-

The scanning of a patterned fabric is illustrated in Fig. '7 of the Vdrawings wherein the reference numeral 101 designates a fabric having pattern stripes 102 therein. Phototubes 5.03 and 104, which scan the fabric 101, are

spaced apart a distance equal to an integral number of widths between the pattern stripes 102 so that each of.

also applicable to other types of textile machinesand to various other equipments wherein it is desired to` employ variations in light intensity for control purposes,

it is to be understood that the foregoing detailed` description is given merely by Way of illustration and/that many variations may be made therein without departing from the spirit of our invention.

Having described our invention, what we desire to secure by Letters Patent is: i

l. A photoelectric stop motion, comprising a pair,

of phototubes, means for traversing said phototubes across an illuminated textile fabric to scan the same, and operatively connected to the phototubes, means responsive to the difference in signal from the phototubes when 'on of the phototubes scans a fabricdefect.

2. A photoelectric stop motion, comprising a pair of phototubes, means forv traversing said phototubes across an illuminated textile fabric to scan the same, and operatively connected to the phototubes an amplifier responsive to the difference in signal from the phototubeswhen one y of the phototubes scans a fabric defect.

3. A photoelectric stop motion, comprising a phototube, a preamplifier tube operatively connected to said phototube, means for traversing said phototube and said preamplifier tube across an illuminated fabric to scan the same, and operatively connected to the preamplifier tube an amplifier responsive to the difference in the signal from the phototube when the phototube scans a fabric defect.

4. A photoelectric stop motion, comprising a pair ofl phototubes, preamplifier tubes operatively connected to said phototubes, means for traversing said phototubes and said preainplier tubes across an illuminated textile fabric to scan the same, and operatively connected to the preamplifier tubes an amplifier responsive to the difference in the intensity of the signal from the phototubes when one oi the phototubes scans a fabric defect. 5. A photoelectric stop motion, comprising a phototube, means for traversing said phototube across an illuminated textile fabric to scan the same, and means" controlled by the position of the phototube for rendering the stop motion inoperative.

6. A photoelectric stop motion, comprising a pair of phototubes, means for traversing said phototubes across an illuminated fabric to scan the same, operatively connected to the phototubes an amplifier responsive to the difference in the signal from the phototubes when one of the phototubes scans a 'fabric defect, and means con-- trolled by the position of the phototubes for rendering l the stop motion inoperative.

7. A photoelectric stop motion, comprising a phototube means for traversing said phototube across an illuminated fabric to scan the same, and operatively connected to the phototube an amplifier responsive to a change in the signal from the phototube, said amplifier tending toward equilibrium whereby it automatically compensates for any slow changes in the signal from the phototube and prevents spurious operation of the stop motion.

8. A photoelectric stop motion, comprising a pair of phototubes, means for traversing said phototubes across an illuminated fabric to scan the same, and operatively connected to the phototubes an amplifier responsive to the difference in the signal from the phototubes when one of the phototubes scans a fabric defect, said amplier tending towards equilibrium whereby it automatically compensates for any slow changes in the signal from the phototubes and prevents spurious operation of the stop motion.

9. A photoelectric stop motion, comprising a phototube, means for traversing said phototube across an illuminated fabric to scan the same, and operatively connected to the phototube an amplifier including means for comparing the signal from the phototube with a reference voltage whereby signals below a predetermined value will not cause operation of the stop motion.

l0. A photoelectric stop motion, comprising a pair of phototubes, means for traversing said phototubes across an illuminated fabric to scan the same, and operatively connected to the phototubes an amplifier which is responsive to the difference in the signal from the phototubes when one of the phototubes scans a fabric defect including means for comparing the difference in signals from the phototubes with a reference voltage whereby a difference in signals below a predetermined value will not cause operation of the stop motion.

ll. A photoelectric stop motion, comprising a phototube, means for traversing said phototube across an illaminated fabric to scan the same, and operatively connected to the phototube an amplifier responsive to a change in the signal from the phototube, said amplifier including means for differentiating a signal from the phototube whereby both a negative and a positive pulse are produced when the phototube scans a fabric defect.

l2. A photoelectric stop motion, comprising a pair of phototubes, means for traversing said phototubes across an illuminated fabric to scan the same, and operatively connected to the phototubes an amplifier responsive to the difference in the signal from the phototuoes when one of the phototubes scans a fabric defect including means for differentiating the dierence in the signal from the phototubes whereby both a negative and a positive pulse are produced when the phototubes scan a fabric efect.

13. A photoelectric stop motion, comprising a phototube, means for traversing said phototnbe across an illuminated fabric to scan the same, and operatively connected to the phototube an amplifier including means for differentiating a signal from the phototube whereby both a negative and a positive pulse are produced when the phototube scans a fabric defect, and means for selec- 'tively amplifying pulses of one polarity.

i4. A photoelectric stop motion, comprising a pair of phototubes, means for traversing said phototubes across an illuminated fabric to scan the same, and operatively connected to the phototubes an amplifier responsive to the difference in the signal from the phototubes when one of the phototubes scans a fabric defect including means for differentiating the difference in the signals from the phototubes whereby both a negative and a positive pulse are produced when the phototubes scan a fabric defect, and means for selectively amplifying pulses of one polarity.

lY A photoelectric stop motion, comprising a phototube, means forrtraversing said phototube across an illuminated fabric to scan the same, and operatively connected to the phototube an amplifier responsive to a 1G change in the signal from the phototube, said amplifier including filtering means for eliminating undesired signals.

16. A photoelectric stop motion, comprising a pair of phototubes, means for traversing said phototubes across an illuminated fabric to scan ,the same, and operatively connected to the phototubes an amplifier which is responsive to the difference in the signal from the phototubes when one of the phototubes scans a fabric defect including filtering means for eliminating undesired signals.

t7. A photoelectric stop motion, comprising a phototube, and means for traversing said phototube across an illuminated fabric to scan the same, said traversing means including shock-absorbing means to reduce the forces on the phototube when the direction of traverse is reversed.

i8. A photoelectric stop motion, comprising a pair of phototubes, means for traversing said phototubes across an illuminated fabric to scan the same, and operatively connected to the phototubes an amplifier responsive to the difference in the signal from the phototubes when one of the phototubes scans a fabric defect including a circuit in which the signals from the phototubes are compared.

i9. A pliotoelectric stop motion, comprising a pair of phototubes, means for traversing said phototubes across an illuminated fabric to scan the same, and operatively connected to the phototubes an amplifier responsive to the difference in the signal from the phototubes when one of the phototubes scans a fabric defect including a circuit containing a series condenser in which the signals from the phototubes are compared whereby both a negative and a positive pulse are produced when one of the phototubes scans a fabric defect.

20. A photoelectric stop motion, comprising a pair of phototubes, n eans for traversing said phototubes across an illuminated fabric to scan thesarne, and operatively connected to the phototubes an amplifier responsive to the difference in the signal from the phototubes when one of the phototubes scans a fabric defect including a circuit containing a series condenser in which the signals from the phototubes are compared whereby both a negative and a positive pulse are produced when one of the phototubes scans afabric defect, and means including an amplifier tubehaving a high negative bias and an amplifier tube having a slight negative bias connected in series for selectively amplifying the positive pulse.

21. A photoelectric stop motion, comprising a pair of preamplifier tubes each having a cathode, an anode and a control electrode so connected that the potential of the cathode follows the potential of the control electrode, a pair of phototubes each havingl an anode connected to the anode of one of the preamplifier' tubes and a cathode connected to the control electrode of said preamplifier tube, a pair of electrical shields each enclosing a phototube and connected to the cathode of the preamplifier tube to which the cathode and anode of said phototube are connected, means for traversing said preamplifier tubes and said phototubes across an illuminated fabric to scan the same said traversing means including shock-absorbing means to reduce the acceleration on the preamplifier tubes and phototubes when the direction of traverse is reversed, means controlled by the position of the carriage to render the stop motion inoperative, and operatively connected to the preamplifier tubes an amplifier responsive to the difference in the signal from the preamplifier tubes when one of the phototubes scans a fabric defect including a circuit containing a series condenser in which the signals'from the phototubes are compared whereby both a negative and a positive pulse are produced when one'of thephototubes scans a fabric defect, means including an amplier tube having a high negative bias and an amplifier tube having a slight negative bias for selectively amplifying the positive pulse, means for lengthening said positive pulse, and filtering means for eliminating undesired signals.

22. A photoelectric device, comprising a pair of phototubes and operatively connected to the phototubes an amplifier responsive to the difference in the signal from the phototubes when the lillumination on one of the phototubes is changed including means for suppressing a dilerence in signals below a predetermined amplitude.

23. A photoelectric device, comprising a phototube and operatively connected to the phototube an amplier including means for differentiating a signal from the phototube whereby both a negative and a positive pulse are produced from such signal, and means for selectively amplifying pulses of one polarity.

24. A photoelectric device, comprising a pair of phototubes and operatively connected to the phototubes an amplifier responsive to the difference in the signal from the phototubcs when the illumination on one of the phototubes is changed including means for differentiating the difference in the signal from the phototubes whereby both a negative and a positive pulse are produced from such difference, and means for selectively amplifying pulses of one polarity.

25. A photoelectric device, comprisingl a pair of phototubes, and operatively connected to the phototubes an amplifier responsive to the dilference in the signal from the phototubes when the illumination on one of the photombes is changed including filtering means for eliminating signals having a frequency outside a predetermined range.

26. A photoelectric device, comprising an ampliier tube having a cathode, an anode and a control electrode so connected that the potential of the cathode follows the potential of the control electrode, a phototube having an anode connected to the anode of the amplifier tube and a cathode connected to the control electrode of the amplifier tube and an electrical shield enclosing said phototube connected to the cathode of the amplifier tube.

27. A photoelectric device, comprising a pair of phototubes and operatively connected to the phototubes an amplifier responsive to the dilerence in the signal from the phototubes when the illumination on one of the phototubes is changed, including a circuit containing a series condenser in which the signals from the phototubes are compared whereby both a negative and a positive pulse are produced when the illumination on one of the phototubes is changed, and means including a amplii'ier tube having a high negative bias and an amplifier tube having a slight negative bias connected in series for selectively amplifying the positive pulse.

28. A photoelectric device, comprising a pair of preamplifier tubes each having a cathode, an anode and a control electrode so connected that the potential of the cathode follows the potential of the control electrode, a pair of phototubes each having an anode connected to the anode of one of the preamplifier tubes and a cathode connected to the control electrode of said preamplifier tube, a pair of electrical shields each enclosing a phototube and connected to the cathode of the preamplier tube to which the cathode and anode of said phototube are connected, and operatively connected to the preamplifier tubes an amplifier responsive to the diiference in the signal from the preamplifier tubes when the illumination on one of the phototubes is changed including a circuit containing a series condenser in which the signals from the phototubes are compared whereby both a negative and a positive pulse are produced when the illumination on one of the phototubes is changed, means including an amplifier tube having a high negative bias and an amplier tube having a slight negative bias connected in series for selectively amplifying the positive pulse, means for lengthening said positive pulse, and ltering means for eliminating undesired signals.

29. A photoelectric stop motion, comprising an aniplier tube having a cathode, an anode and a control electrode so connected that the potential of the cathode follows the potential of the control electrode, a phototu'oe having a nanode connected to the anode of the amplifier,V

phototube connected to the cathode of the amplilier tube,

means for traversing said phototube and said preamplifier tube across an illuminated fabric to scan the same and operatively connected to the preamplifier tube an ampliiier responsive to the difference in Vthe signal from the phototube when the phototube scans a fabric defect.

30. A photoelectric stop motion, comprising a pair of preamplifier tubes each having a cathode, an anodeand a control lelectrode so connected that the potential of the cathode follows the potential of the control electrode, a pair of phototubes each having an anode connected to the anode of one of the preamplilier tubes and a cathode connected to the control electrode of said preamplifier tube, a pair of electrical shields each enclosing a phototube and connected to the cathode of the preamplifier tube to which the cathode and anode of said phototube are connected means for traversing said phototubes and said preamplifier tubes acrossanfilluminated fabric to scan the same, and operatively connected to the preamplifier tubes an amplifier responsive to the difference in the intensity of the signal from the phototubes when one cf the phototubes scans a fabric defect.

31. A photoelectric stop motion for patterned textile fabrics, comprising means for illuminating the fabric, a pair of phototubes spaced apart a distance equal to an integral number of pattern Widths whereby each phototube views a corresponding portion of the pattern, meansk for traversing said phototubes across said fabric to scan the same, and operatively connected to the phototubes an amplifier responsive to the difference in signal from the phototubes when one of the phototubes scans a fabric defect.

- 32. A photoelectric device, comprising a phototube the phototube, and means connected to the electrodesfof the phototube and also connectedto the electrical shieldfor causing the potential of the electrical shield to follow the potential variations of the phototubc.

References Cited in the le of this patent UNITED STATES PATENTS 1,680,348 Thilo Aug. 14, 1928 1,762,748 Smith June 10, 1930 1,919,888 Hough July 25, 1933 2,044,471 Dodd et al. June 16, 1936 2,065,758 Shepard Dec. 29, 1936 2,139,474 Shepard, .lr Dec. 6, 1938 2,153,202 Nicols Apr. 4, i939 2,193,590 Gulliksen Mar, 12, 1940 2,207,048 Campbell Iuiy 9, 1940 2,231,621 Goodridge Feb. 11, 1941 2,290,257 Stanley June 21, 1942 2,298,466 Cooley Oct. 13,1942 2,299,260 Sivian Oct. 20, 1942 n 2,320,977 Nicokori June 1, 1943 2,336,633 Parson Dec. 14, 1943 2,339,053 Coleman Jan. 11, 1944 2,379,233 Hood lune 26, 1945 2,381,414 Wilkie Aug. 7, 19,45 2,416,215 .Rath Feb. 18, 1947 2,442,240 Hooker et al. May 25, 1948 2,450,996 Seney Oct. 12, 1948 2,488,430 Oifner Nov. 15, 19.49 2,517,554 Frommer Aug. 8, 1950 2,559,173

Shawhan July 3, 

1. A PHOTOELECTRIC STOP MOTION, COMPRISING A PAIR OF PHOTOTUBES, MEANS FOR TRAVERSING SAID PHOTOTUBES ACROSS AN ILLUMINATED TEXTILE FABRIC TO SCAN THE SAME, AND OPERATIVELY CONNECTED TO THE PHOTOTUBES, MEANS RESPONSIVE TO THE DIFFERENCE IN SIGNAL FROM THE PHOTOTUBES WHEN ONE OF THE PHOTOTUBES SCANS A FABRIC DEFECT. 